Students get to Elementary School with a series of misconceptions which are not necessarily in agreement with the scientific knowledge. Misconceptions result from the student's attempts to understand their previous experiences resulting from their interaction with their environment and they must be taken into account in educational practice to design appropriate instructional strategies that will impulse their evolution into more scientific-academic concepts. This research aims to detect the initial knowledge that twenty-one fifth grade Elementary Education students (ages ranged: 10-11 years old) have about material composition. A questionnaire was used as an instrument to determine initial misconceptions. Based on the students' answers, important misconceptions were identified, and an appropriate instructional strategy was design to foster the students' conceptual change about the studied topic. A post-task questionnaire conducted after the instruction revealed the suitability of the proposed instructional design.